A "Tailor" is a role type of crew member in the game.

I think that the easiest way to recruit a "Tailor" to join your crew is to follow these instructions:

Decorate a room with very wealthy objects and then hang a "Colony Deed" on the wall (you can get one at "Froggy Furnishings" at the "Outpost.")

From there you will spawn an NPC character. If you decorate the room with the most of the same objects that you see in the screen cap I am sharing in this post, then you will very likely get a "Socialite" or "Philanthropist" NPC for a tenant (either of them can become a tailor).

The "Philanthropist" tenent looks like Mr. Monopoly (if you remember him form the Monopoly boardgame box, he has a white mustache and top hat). Once you get a "Philanthropist" tenent. Then do a few quests for him, and he will ask to join your crew.
Philanthropist NPCs always become a "Tailor" when they join your crew.

It's a super weird gameplay-story-concept that a rich Philanthropist would want to become a Tailor when he asks to join your crew, but that is how it works.
The instructions I gave you are how to recruit a tailor in the regular game (vanilla-mode) with no cheats or Mods.

...But, if you are having trouble recruiting a "Tailor" following the instructions, then you can always add the "NpcSpawner+" mod or Job Offers.

It allows you to make custom NPCs. You can customize the NPCs just like you would when creating a new character, using the mod's new "NPC Maker 3000" object. You can then choose an "NPC Type" to make an NPC be any type of crew member. Under the "NPC Type" tab in the NPC Maker 3000, choose: CrewMemberTailor, and it will spawn a "Tailor" that you can customize yourself.
For Job Offers, you can craft employment contracts to hire NPCs with any job.

Thanks to Loial-the-Ogier who wrote these explanations, I just pin this here ;)