next past tense? for example...

my question is if i use “my next” does that automaticly mean i had one before?

for example:

my next dog will be a golden retreaver.

By saying “my next” does that mean i had a dog before? or is there a diffent way i should say it? or did i use it the right way?

Yes and no. You had at least one before.

It’s also possible to say “My next dog will be a golden retriever” when you already have a dog at present.

O yes. Next doesn’t necessarily extinguish the preceding.