should i change my oil before a coolant flush?

What is your question?

I was told that i may have a cracked head or a blown head gasket because i have water in my engine. Meineke wants to charge me 8-10K to replace the engine, which I REALLY can't afford. I have a sealant for a temporary repair, but I'm not sure if I should change my oil first before doing a coolant flush to add the sealant. the brand of sealant that i chose is Bar's Leaks Block Seal Head Gasket Sealant. The reviews I've seen look really good, but I hope I'm not wasting money trying to fix this. Any suggestions? could it be a water hose or water pump issue?

What makes this problem better or worse?

Car shutters as soon as I start it up and shuts off after a while from overheating I'm guessing.

How long has your 2016 Ford Edge had this problem?

one month