You can't move a character to another ruleset in WoW Forever. If you picked the wrong one, the fix is to make a new character on the right ruleset. Blizzard's ruleset post says you play under a different ruleset by creating a new character there. It doesn't offer transfers.
Your options
- Reroll early. The sooner you do it, the less you lose. Collections and Legacy Points are account-wide across rulesets, per Blizzard's post.
- Stay and find your people. Guild recruitment posts on Blizzard's forum say which ruleset they're on, so you can see who's where.
- Play both. Keep your first character and level a second one on the other ruleset.
If you're on Roleplay
Roleplay rulesets have naming and behaviour rules. A busy forum thread about RP names and guilds reminds players that names breaking the rules can be reported. If you don't want an RP-style name, the Normal ruleset is the better fit.
If you're on PvP
You're locked to one faction there, and a faction can be temporarily unavailable. If your friends are on the other faction, you'll need a new character, whatever you do.
Choosing next time
Our ruleset guide explains each one. Agree with your friends before anyone makes a character, because you can only group with the same ruleset and faction.