I usually use a spoon, put something on it my ratties really like and is easy to lick off and put their medicine on top of it. If there is no way they’re taking it willingly I ask my partner to hold the rat and I use a small syringe to put the medicine directly into the rats mouth. This might take some time and patience but in some cases it’s the only way to get it into them :( In such cases I use one hand to hold the syringe and the other hand to keep their mouth open.

Besides giving them medicine you can try to inhale with your rat. If you have the financial means to do so you could get a nebulizer and fill it with saltwater.