It is best just to remake the whole part. If you can’t figure out the dimension of something ask, but don’t ask for all the dimensions please. Stl’s are easy to add to but difficult to subtract from. If you are adding to a part please keep in mind support doesn’t work well for most people and the print orientation I designed is extremely important.
In the beginning a lot of people were sticking the parts together to print as a single part to “increase strength” all they made were weaker parts that required a ton of support.