It's because you need to change the deleted property on the entity patient that has the user id.

Go to the patient entity and change the attribute that has the user id reference the deleted property to ignore in case you want to stay with the record or change to delete to remove it permanently.

You will see something like this

The permanent rule makes you not able to delete it and that's why you get that error.

Have a look at this link.

Márcio

Hello Kundan Chauhan,

That erros occurs when you try to delete a record that has a foreign key that is a primary key on a different record, in this case the ID. 

To be able to delete that item you should first delete all the records that use that items ID as Foreign Key or 

set the Delete Rule your Entities to Ignore.

For more information on Delete Rules please check out this link.

Hope it helps ! 

Paulo Rosário