The normal steps for an online LMS event in lichess are as follows
Team Selection
1 hour or more before the match time, the 2 captains select their teams but can't see each others team. The team selection option is reached by clicking on the match result from the fixtures list. The players lichess id is shown after the name in square brackets. If its not shown, get it added to the LMS by your league organiser 
See pairings
Ifs its an hour or more before the match, you won't see the pairings yet, just this message. An hour before the match the pairings become visible Click on the link that is your opponents lichess id. This will take you to lichess where you can issue the challenge as per below. (note that clicking the TV icon will take you to the players current game - this can be used to watch their game in progress)
Challenge your opponent
You should see the lichess id of your opponent to the left. If you see SIGN IN on the top right, then you need to click on it to login.
You should then see your lichess user name at the top right. If your opponent does not have a green dot next to their name then they are not logged in. To challenge your oppnent click on the crossed swords shown by the black arrow (not the ones on the top line, which is where you view your own challenges) Then set the time limit as show. Click rated. Then if your are the white player issuing the challenge, click on the white king.