Opening books, courses etc are generally a waste of time at 900 level.
One thing you can do is watch master games with commentary in your opening, something like Agadmator's channel or Naroditsky (assuming your opening is one that masters ever play). Over time, this lets you build up a general sense for what the right ideas are and how the opening ought to be played.
Lichess Explorer is a great tool. Go here on a computer. Click the book icon down near the bottom right. Mess about with switching between master/Lichess database and changing the settings and stuff until you understand what it does. After you play a game, go have a look. See who deviated from commonly played moves. If it was your opponent, opening theory won't help you. If it was you, see what masters play in that position, see what performs well for other players of your level (noting that Lichess ratings are around 300 points higher than equivalent chesscom ratings). Try to understand why the theory moves are better than your move. If it's a complicated position, post and ask about it.
ChessTempo has a free repertoire builder, so if you want, you can start building up lines in the opening and it will train you on them.
How exactly do you go about learning a chess opening?
Which books on chess openings are recommended?