If the suck reflex cannot be stimulated, tube-feeding will be required at first. Feed 1 – 1.5 ml glucose solution (depending on kitten’s size) every 30 minutes. If and as its condition improves gradually increase the amount and decrease the frequency. Gradually introduce milk feeds. If the kitten recovers fully it can be returned to the litter.
If the mother is placid and co-operative, you can try "aided suckling". Express a drop of milk from one of her teats and place the kitten on the teat (making sure it takes the teat into its mouth, just as you would if bottle feeding it). Hold it in place and stimulate it to suckle by stroking either side of its muzzle. You may also have to "tread" the mammary area with your fingers. The kitten should have short, frequent aided suckling session until it can suckle unaided. After each aided suckling session, weigh the kitten to check that it has fed. If not, you will have to bottle -feed or tube feed it.
A kitten that fails to recover or to show improvement within 24 hours is unlikely to survive; its brain and other organs have probably been irreparably damaged by lack of oxygen.