Set Tenant Id to custom auth variable

While setting-up OAuth 2.0 authentication I am passing Tenant Id as additional parameter with the Code in the authorisation get url. Zapier is fetching the code from the url and automatically set the value in the bundle variable named as code. I also want zapier store the tenant id at the same time from that url to another bundle variable named as tenant, so that I can use this bundle tenant variable for first token generation api call and for the rest api call too.