Can a request for an extension 2018 tax year to prepare?

go to www.irs.gov/payments and "Make a payment"

select Reason: Extension

pay any amount ($5.00 will do}.   your request is automatically approved.

Make a note of your payment  amount so you can claim credit for that.

the amount should be the balance of your tax liability to avoid penalties.
If you have to guess, overestimate. you'll get it back when you file.