Fantrax downloads its player list as a CSV file. Filtered on players who have a team, that file fits the Estrade template.

The Fantrax export

In your league, click Players.
Change the Status/Team filter from "All Available Players" to "All Taken Players": only the players who have a team remain.
Click the download button to the right of Find Player. The file starts with the columns ID, Player and Team.
Open it in Excel or Google Sheets. Player becomes joueur, Team becomes equipe_lnh, and the position column, if there is one, becomes position. A dual position like "C,LW" works: Estrade keeps the first position it recognizes.
The column that names each player's team in your league becomes pooler. If the file doesn't have one, download each team instead: a team's page also has a download arrow. Then add the team name to its rows.

Before importing, check that the goalies are in the file.

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. Note each team's total in your Fantrax league standings before the import.

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 the download doesn't work, 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.