I find it hard to believe someone who has access to a cigarette filter doesn't have access to a single unused Q-Tip. A pack of Q-Tips brand or generic can be had for less than a dollar.
I assume you mean how to remove Heroin from old cottons. There is no safe way to do so. The only way cottons have any dope at all in them is if you did a shitty job sucking the liquid out the first time. Saving old cottons is horribly unhealthy, the fungal and bacterial microbes that swarm the thing are waiting to get access to your body and cause horrible health problems.
The safest thing to do is when you initially use a cotton to filter a shot, after you have sucked everything out of it, use a second syringe with 10-30 units of water to squirt clean water onto the (just used) cotton, then suck up through it again. This should remove most if not all of anything that could be left behind on it.
But this should be done immediately after you have used the cotton, not days or weeks or months after the fact. A lot of addicts like to save cottons, but it's pointless and horribly unsafe. Do not use cigarette filters at all.