Setup different SSH keys for multiple git remotes: https://twitter.com/jgcmarins/status/1234881259316404229

config

# GitHub.com
Host github.com
  Preferredauthentications publickey
  IdentityFile ~/.ssh/id_rsa_github

# GitLab.com
Host gitlab.com
  Preferredauthentications publickey
  IdentityFile ~/.ssh/id_rsa_gitlab

instructions.md

1. You can generate them using this command: ssh-keygen -o -t rsa -b 4096 -C "email@example.com"
2. There will be a question about the file name. Choose different file names so it won't override the existing ones.
3. It's also important to keep those files with read/write permission only for you:

$ sudo chmod 0600 ~/.ssh/id_rsa_github

$ sudo chmod 0600 ~/.ssh/id_rsa_github.pub