OK, here is a suggestion.

The fuel station is currently mapped as a floating node.  This is okay, this is a good way to map things.

You can add the car-wash, also as a floating node.  The easiest way for a simple edit like this is through the iD editor, directly from the osm.org website (through the Edit button).  Add a floating point and tag it as a car-wash.

Both the fuel station and the car-wash can be moved to their accurate location, if you know them well.
https://www.mapillary.com/app/?pKey=715968764555637

Each tag can add some additional tags: the name of the operator, self_service=yes/no and opening hours are probably the most useful information for them.

(A more advanced scheme is to map access roads.  Here is an example: https://www.openstreetmap.org/node/9423408199, but as I said, this is a bit more advanced because it requires some knowledge of how to draw roads across buildings without damaging the map.  I can show you that at a later stage.)