First, make sure that your plan supports custom onboarding processes.
Any contracts that you will like added to Liquid for signature or data entry during onboarding must be in Microsoft Word format with the appropriate signature fields added and with the appropriate formatting for custom data fields.
Next, find an existing process that looks similar in structure to your custom process, and clone that process.
Edit the cloned process to add your custom contract and custom steps. When adding your custom contract, make sure that your additional data fields are added to the appropriate step in Liquid and formatted properly in Microsoft Word.
Make sure to press Close to save your changes on any onboarding step, and then also press Save Changes to save the changes to your onboarding process.