How delete old item in a list and insert a new record instead with the updated data in SharePoint Designer?

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Hi,

I need to create a workflow in SharePoint Designer 2010 that will delete list items and update the records with new data.

When a new item is created the workflow will be triggered to check if the list already have a record with the same column (Contractor) value , if the new contractor doesn't exist in the list the workflow need to create the record as normal.

If the new contractor is already in the list, the workflow needs to do a calculation (add 1 to their current Rank(column)).

My intention is to create a list of 5 contractors with rotation (ranking 1 then go to 2, ranking 2 then go to 3 ..... if ranking 5 then go to 1)

The issue I am having is that every time I try to access a value in the workflow, I get a message that says "can't return a single value, will take the first one" something like that.

Can anyone give the steps to do this?

Thanks.