pat From Collins English Dictionary:
If you pat something or someone, you tap them lightly, usually with
your hand held flat. ...........
a quick, gentle tap, touch, or stroke with the hand or some flat
Although this definition and most definitions refer to using the hand held flat, or the palm of the hand, one can pat something, especially something that is small, with the tip of a finger.
I pat a piece of adhesive tape on the sample with the tip of my finger
(to make insects stick onto it), and examine it (and the insects on
it) under the lens of a microscope.
In your example, you can leave out "with the tip of my finger" if you want, or, if you don't use your finger, replace that phrase with what you do use, for example "..with a Q-tip..."