In a multi-tenancy with a single client setup, the recommendation for this configuration is to use different sub domains or pathnames for each of your different tenants login pages and dynamically update Lock configuration.
You can see detailed info here:
Alternatively, in case the users have different usernames, you can make use of the [connectionResolver] (GitHub - auth0/lock: Auth0's signin solution) function of Lock, which allows you to choose which connection to use based on the username information