Go to CRM > CRM Forms > and scroll to Preset Forms.
You can change the domain in the settings of the preset form Contact Info. Press Edit buttton.
Open the form Contact Info > click on the gear icon > go to Page Settings.
Go to the Site settings.
Here you can change the site address or connect your own domain.
To change the site's subdomain, click on the pencil.
Specify a subdomain. If the name is already taken, select another one.
Save the settings. After that, the form will be available at the new address. The subdomain will change for all CRM forms.