PoolExpert's FAQ describes no export of a pool's lineups. Its "Tout en un" (all in one) page shows the standings and each participant's full lineup on a single page: that's the one to copy.

The PoolExpert "Tout en un" page

Sign in to your pool on PoolExpert. In the pool menu, on the left, open Tout en un. The page is titled "Classement" and, according to PoolExpert, it "réunit le classement du pool et l'alignement complet de chaque participant" (brings together the pool standings and each participant's full lineup).
Under each participant's name, a table lists their players with the columns T (the position in the pool), Rnd (the round), Nom (name) and Ville (the NHL team, as an abbreviation). Select those tables, copy them and paste them into Excel or Google Sheets.
Arrange the columns: the participant's name becomes pooler, Nom becomes joueur, Ville becomes equipe_lnh and T becomes position. Delete the stats columns.

In PoolExpert's demo pool, the T column gives D or G to defensemen and goalies, and stays empty for forwards: leave the cell empty. It's T for a drafted NHL team, like "Golden Knights" (VGK): write EQ in position and keep the abbreviation in equipe_lnh, where Estrade reads the team. Your lineup then needs a team slot. Some teams are written with two letters there, like SJ or NJ. Estrade flags them without blocking; write SJS or NJD to avoid the warning.

The Estrade template

Estrade reads a five-column table, one row per owned player, with this header and in this order:

pooler,courriel,joueur,equipe_lnh,position

pooler: the team name, 30 characters at most, the same on all its rows.
courriel: the email address, optional, one per team. Without an email, you manage the team yourself.
joueur: the player's first and last name. Accents and capitals don't matter.
equipe_lnh: the NHL team, as an abbreviation (MTL) or the club name (Canadiens). It tells apart players with the same name. A team Estrade doesn't recognize gives a warning, not an error.
position: C, LW, RW, D or G. AG, AD, L, R, F and A are also read, and the cell can be left empty. EQ means an NHL team, if your lineup has a team slot: Estrade then reads the team in equipe_lnh.

No other columns: delete the rest. Save as CSV (commas, semicolons or tabs), or copy the table from the spreadsheet and paste it into Estrade.

The import in Estrade

In My pools, click Start a pool, choose Already-drafted pool and create the pool. You land on the import screen.
In Pool settings, copy the rules of your old pool: lineup, cap, scoring. The import screen opens again from the pool menu, Import a pool in progress.
Choose your file under CSV file, or paste your table under Or paste your table and click Read the table.
Under To fix, each problem gives its row: choose the right player, search for them, or click Remove the row. Nothing is saved while a problem remains.
Enter the points already earned, then click Import the pool. The Season Pass is paid before this step. Each pooler with an email in the file gets an invitation tied to their team. The import can't be undone.

A player missing from the NHL catalogue, like an AHL prospect, can't be imported: remove their row. The details of each screen are in the guide, under import a pool in progress.

Points already earned

Estrade doesn't recalculate the season: games count from the day of the import. On PoolExpert, the same "Tout en un" page gives each participant's points, in the PPts column.

In a points pool, enter under Starting points each team's total, up to yesterday's games, with a Reason of 3 to 140 characters. Everyone sees it in the adjustment log.
In head-to-head, enter under Starting record each team's wins, losses and ties, up to the Sunday before the week of the import, with the same Reason. Points scored in earlier weeks are not carried over.

Entering it by hand

If nothing copies cleanly, start from the blank template that Download the template gives on the import screen. Type one row per player: the first and last name are enough. The NHL team and the position can stay empty; Estrade then asks you to choose between players with the same name.

The other platforms also have their page on moving a pool.