unable to add existing parameter to custom payroll flow task

Summary: Need to add the parameter to my existing task in flow pattern

Content (please ensure you mask any confidential information):

We have an existing parameter in our custom payroll flow and we need this same parameter to be linked for one of the task present in payroll flow. But add option is not available to link that parameter here.

Version (include the version you are using, if applicable): 26A

Code Snippet (add any code snippets that support your topic, if applicable):