Hi Jayashri,

If i understood your problem , your were trying to update an value which is associated to other entity.

For this Create a microflow for save button , inside microflow do retrieve entity which your target to update. Followed by update the value to the retrieved entity using change object.

Notes:

Try to check is retrieved object was available i mean created or not if necessary.

If this doesn't helps, provide some more information about your problem with some screen shots if possible.

Regards,

Sathya Reddy