You can create your own personal access token.

Token should be registered with scopes:

• api - For read/write access to the API, including all groups and projects
• repo - For read-only access to the authenticated user's profile through the /user API endpoint, which includes username, public email, and full name

In Jenkins, create a token credential as «GitLab Personal Access Token» or any «StringCredentials» type credential (e.g. «"Secret text"» provided by Plain Credentials plugin or «"Vault Secret Text Credential"» provided by HashiCorp Vault plugin). Human-readable id and description is recommended.

If you have an existing GitLab login and password you can convert it to a token automatically with the help of «Manage additional GitLab actions» in Advanced section of GitLab Servers.