There are many ways to reduce pressure from a foot blister. It depends on where it is on your foot. What gear you have on you. And what you're activity will be up to.
1. Donut Pad
A donut pad to lift the shoe off your heel blister; or to reduce weightbearing pressure from a blister under the ball of your foot.
Here’s the orthopaedic felt I’ve used above for this donut pad. And the tape you’ll need to cover it.
2. Cushioned insole
A cushioned insole for a blister under the ball of your foot (cushioning reduces the force per unit area by spreading the load over a larger area). Read more here.
3. Gel toe protectors
A gel toe protector to cushion a blister between your toes, on top of your toe or on the side of your toe.
Grab you Gel Toe Protector Caps or Sleeves here
Toesocks to cushion a blister between your toes.
Orthotics to reduce pressure from the underside of your big toe. Read more here.
6. Shoes that don't press on your blister
Wearing shoes that don't press on the blister (at all or as much) - like scuffs for a heel blister; or a deeper toebox for a blister on top of your toe, or a wider toebox for a blister on the outside of your little toe, or cutting out the toebox of your shoe for a blister on the top of one of your toes!
Lacing your shoes tighter to stop your toes (one of which has a blister under its nail) from slamming into the end of your shoe when you're going downhill.
8. An altered gait
Walking or running differently to reduce weightbearing pressure on a blister. For example, avoiding a heel strike if you have a blister under your heel. Or if your event allows it (and you have them handy), using poles can help you adjust your gait to reduce the propulsive force required from your foot, reducing pressure on the ball of the foot and toes.
9. Put your feet up to reduce swelling
If your feet are swollen and this is putting extra pressure on a blister somewhere on your forefoot (toes / ball of foot), put your feet up when you can, to allow fluid to drain.
Non-weightbearing, including pulling out of the race if it's painful enough or if there is significant risk to your health (eg: deroofed, blood blister, infected). While I'd love to put up a picture of a DNF-worthy blister, I get complaints about such images. If you want to see a few blisters I'd consider too difficult or risky to manage mid-race, check out Cape Wrath Ultras blister article: http://www.capewrathultra.com/news/2016/01/13/Guidance_on_Foot_Care_for_Participants_at_the_Cape_Wrath_Ultra/
Before you jump in ...
When choosing a pressure-reduction strategy for your blister, be aware of its potential downsides. For example:
A donut pad on your heel might push your foot too far forward in your shoe, jamming your toes into the toebox.
Toesocks might squash your toes because there's not enough width in the toebox.
Silicone gel toe sleeves might make your skin too sweaty.
Changing your gait to avoid a heel strike, when you normally run with a heel strike, is very likely to make something else hurt and possibly cause injury.
Weigh up the pros and cons!
PS: ENGO patches and lubricants do nothing for pressure. They deal purely with friction [pressure is a vertical force; friction is a horizontal force]. Friction management is super-important in treating blisters.