I want to go into sewing and learn it very well but few men are actually into the business and whenever I see them in their shops I feel discouraged 'cause it doesn't even seem as if they get anything from it. I need your advice, Nairalanders.

Unless you mean those that just sew.
https://en.wikipedia.org/wiki/List_of_fashion_designers?wprov=sfla1

Ignorance can be irritating...mind u there re now called fashion designer
Yomi casual is a fashion designer and he's doing extremely well just pray for Grace

HazardAwka:
I want to go into sewing and learn it very well but few men are actually into the business and whenever I see them in their shops I feel discouraged 'cause it doesn't even seem as if they get anything from it. I need your advice, Nairalanders.

Networking and packaging.

Meet rich people, tell them you're a tailor.
Packaging means wear what you see to promote your work.