If this is a Lichess game, just paste the game link in your message, and it will appear like this:
If not, import the game in Lichess by using the "Tools - Import Game", paste your PGN, and then paste the game URL here.
If you only have a FEN, you can still write the Lichess Analysis URL link in your message:
lichess.org/analysis/standard/r1bqkb1r/1ppp1ppp/p1n2n2/4p3/B3P3/5N2/PPPP1PPP/RNBQ1RK1_b_kq_-_3_5