When you go to create a league on Sleeper, you'll find that we only support leagues that have an even number of teams.
If you want to carry on with an odd number of teams, it can be done, but will just take some manual work.
We really encourage you to try to get 1 other team to join if you could, but if not, here are some options.
First, you'll have to have an unassigned team to get you to that even number.
As commissioner, set the draft order and put the empty team last. Then, prior to the draft, access your draftboard and click on an individual pick for that team. Assign them a very lowly-ranked player, and do this for all of their picks. These players will act as placeholders, so that when the draft begins, that team will be skipped over.
Once the draft is complete, the commissioner can use the commish tools in the mobile app to drop all of that team's players.
Now, you have an empty team for the rest of the season, so whoever face them, will get an automatic win that week.
If you don't want them to get an automatic win, use the commish powers on the web app, and adjust the score of their matchup at the end of the week. If you put the two teams at the same number, you can have them result in a tie.
We may support leagues with an odd number of teams in the future, but for now, you'll have to use a workaround.