Go https://teechip.com/ and make a seller account and design phone cases for sale I basically downloaded anime wallpaper from google and designed each case 

you could use supreme or anything except louis vuitton patterns because of Copyright issues 

take advantage of the tik tok free ads up to $2000 

https://www.tiktok.com/business/en/ 

and advertise your tee chip shop 

then

make free ads with the google ads credits up to $150

focus on youtube ads and discovery ads you could watch a youtube video on how you make effective ads depending on your product 

https://ads.google.com/intl/en_us/lp/coupons/ 

cheers