How to use the netlify-cms-backend-gitlab.GitLabBackend function in netlify-cms-backend-gitlab

};
      const apiConfig = {
        api_root: `${this.gatewayUrl}/${this.backendType}`,
        branch: this.branch,
        tokenPromise: this.tokenPromise,
        commitAuthor: pick(userData, ['name', 'email']),
        squash_merges: this.squash_merges,
        initialWorkflowStatus: this.options.initialWorkflowStatus,
      };

      if (this.backendType === 'github') {
        this.api = new GitHubAPI(apiConfig);
        this.backend = new GitHubBackend(this.config, { ...this.options, API: this.api });
      } else if (this.backendType === 'gitlab') {
        this.api = new GitLabAPI(apiConfig);
        this.backend = new GitLabBackend(this.config, { ...this.options, API: this.api });
      } else if (this.backendType === 'bitbucket') {
        this.api = new BitBucketAPI({
          ...apiConfig,
          requestFunction: this.requestFunction,
          hasWriteAccess: async () => true,
        });
        this.backend = new BitbucketBackend(this.config, { ...this.options, API: this.api });
      }

      if (!(await this.api.hasWriteAccess())) {
        throw new Error("You don't have sufficient permissions to access Netlify CMS");
      }
      return { name: userData.name, login: userData.email };
    });
  }