git get error: "Peer's Certificate issuer is not recognized"

2020-03-26 ssl gitlab

When I run something like: git clone from part of the clients, I get the error:

Peer's Certificate issuer is not recognized

I saw 2 main solution:
1. User can set export GIT_SSL_NO_VERIFY=true 2. to install root certificates

I would like to solve the problem to all the users.
I did not understood how to install the root certificate and where I configure Gitlab to use it. Is there url to clear instruction?