Where we should save refresh token and access tokens?

Question

im'm making a fullstack application with next js.

i want to use both refresh token and access token with JWT.

this is very important. I'm using jwt and next js. not oauth etc...

i had maked my tokens in backend but i don't know where i should save them.

both of them must be saved in cookie? i don't know i should save refresh token as a cookie or access as a cookie. and when i saved one of them as a cookie, another one should be saved where securly...

i am looking some websites they have refresh and access token system but all of them, have just one token in cookies part. when I search in those local storage or cookies, they hasn't another cookie...

thanks for your responses