I registered gitlab runner, but then delete this runner from gitlab admin panel. How i can readd existing runner to gitlab instance?
If you deleted it from inside Gitlab, then you need to create a runner, copy the token that appears on the Gitlab web interface, and then edit config.toml and put the new code in here. Then restart the Gitlab Runner. That should do it.
You cannot register it with the same token that you used previously, because you deleted that from the web interface.
Failing that, follow the instructions on how to register a runner from the Gitlab docs: Registering runners | GitLab