There is a concern that lubricant might block absorption of blood onto the cloth, so the permissibility of moistening a cloth with lubricant is debated. Slightly wetting a bedikah cloth with water, however, is widely accepted. We recommend first seeing if it suffices to wet the cloth with a drop of water and to perform the bedikah very gently.
Using a vaginal moisturizer ahead of time is also permitted. There is no strict time interval, though waiting fifteen minutes between application and checking would seem reasonable. Some moisturizers are long acting, so that the moisturizer could be used much earlier in the day, which may alleviate pressure around the time of the bedikah.
There are those who permit a drop(s) of water-based lubricant, as long as the woman waits long enough for it to be absorbed enough into the fabric so that it will not make the finger moist from the touch. So if the above steps do not suffice, you may use a drop of water-based lubricant.
Please write back with any further questions.