What were the steps done when you encountered false positive results of such testing?

False positive: A result that indicates that a given condition is present when it is not.
An example of a false positive would be if a particular test designed to detect cancer returns a positive result but the person does not have 'cancer.
So, A false positive result is an error, which means the result is not giving you the correct information.
When medical people tell you that you have had a false-positive test or a false-negative test, it does not automatically mean that a mistake was made.
In fact, such a statement actually does not always truly even mean that the result was false.
And the significance of the situation varies upon what kind of test?
1- a "screening test" (a test in search of a disease in a person who does not appear to have it...example: PSA test for prostate cancer),
2- a "diagnostic test" (a test for a specific, particular disease...example = lung cancer...in a person who has a more general finding such as "a spot on the lung"...typical of the specific disease we are concerned about),
3- a "treatment decision test": patient had a stroke which seems to be because a clot traveled to the brain.
Did it come through a patent foramen ovale (PFO)?
4- or a "monitoring test" (a test which helps doctors "keep track" of how you are doing with a known disease...example: hemoglobin A1c in a diabetic).
Thus false positive and false negative ratios may occur and need to be avoided where possible.
Otherwise, we need to repeat the test by taking in consideration avoidance of factors which encounter or interacts with testing materials/ conditions and affect the results.

false-positive results are very rare.
but if it happens it will be done by testing another method, because there are several methods of testing

you must use a specific method and good reagent for famous company then use another method to be certained of your result    

Its a Type2 error in research.

Check your hypothesis again.

make sure your hypothesis is not just opposite to what it should have been.