You can simply create a UI Action, check the form button checkbox which will display the UI action as button, In condition add "current.canCreate();" or if you want to add more validation for the Button visiblity you can and you can refer to the below script:
var gr = new GlideRecord('table_name'); //replace table_name with correct table name
gr.initialize();
gr.field_name1 = current.field_name1;//replace field_name1 with your one of the field name you want to copy
gr.field_name2 = current.field_name2;//replace field_name2 with your one of the field name you want to copy
gr.field_name3 = current.field_name3;//replace field_name3 with your one of the field name you want to copy
gr.field_name4 = current.field_name4;//replace field_name4 with your one of the field name you want to copy
gr.insert();
action.setRedirectURL(gr.getLink());
var link = '<a href="' + current.getLink() + '">' + current.number + '</a>';
gs.addInfoMessage("Record was copied from " + link);
Once the record is copied the you will be redirected to the new record and you will have an info message at the top with the link of old record.
Kindly mark my answer as Correct and helpful based on the Impact.
Regards,
Alok
