You are on the right track. First, you need to create a Lookup that will bring back a specific record. Work on that first. Once you have the lookup working then you just need to do the patch as you are, with a couple changes.
1) You need to patch all the required fields in addition to VarViz. For example, Title: is a requried field in SharePoint so you'll need to patch that too.
2) You need to use the current value of the field when you add 1 to it.
So your code would look something like this.
Set(recordvalue, Lookup(datasource, criteria));
Patch(datasource, recordvalue, {Title: recordvalue.Title, FieldtoIncrement: recordvalue.FieldtoIncrement +1})
