I have created a SAP process automation in SAP BTP cockpit. Is there any way to link this process to a specified button in my Fiori Launchpad?
The question is what you mean with "my" Fiori Launchpad.
Did you mean the one you got provided from your IT?
Than you can't add the SAP Process Automation to Fiori by yourself.
You could ask the administrators to add a link to SAP Process Automation in the Fiori Launchpad Designer.
When you talking about the SAP Launchpad Service and you are the administrator you need to configure that in the Content Manager - this tutorial might help: https://developers.sap.com/tutorials/cp-portal-cloud-foundry-url-applaunchpad.html
I hope my answer helps you.