Your 5K PR is around 22 minutes, right? That's right around 7:05 pace. So your tempo pace is 25 seconds/mile slower, or 7:30/mile.
Tomorrow, run for 5 minutes at this pace. That's 2/3 of a mile, less than 1200 meters. Very doable, and you'll get a feel for the pace.
Next week, do 7 minutes.
Each week, add a minute or two. In 7-8 weeks, you'll be up to 20 minutes.
If it starts to feel too intense, break up the run into 2-3 chunks, like 5-5-5 minutes. Then reduce the number and length of breaks between chunks.
Your target distance is 5K, and you're a long way from racing, so concentrate on getting up to 20 minutes for now. At some point, 7:30 per mile will start to feel too easy, so you'll be able to speed up while still feeling tempo pace.
That is how do do a tempo run.