Hello @Mo. Farid  

Thank you for posting your query in the Nutanix Community. 
Yes, you can covert a Nutanix HC node as a Compute Only node. As mentioned in AHV Admin Guide.  You need first remove the node from the cluster if it's already part of it and need to foundation the node as compute only. 

This section of the Field Installation Guide describes at what step you need to choose the node as Compute Only. 

Once the node is foundation with Compute Only option selected you can use the steps mentioned in  AHV Admin Guide using expand cluster method to add this node to the cluster.