Adding vodka to accidentally diluted Hard Seltzer

[metalhophead]

Hey guys. I brewed a hard seltzer and accidentally added 1 extra gallon to my fermenter. (should have been 5 gallons) Its at 4 pct abv currently and I would like to bring it up to 5 pct. I was told I could add vodka to bring up the alcohol. How in the heck do I calculate how much to add? I was given this calculator, but I can't figure it out. Vinolab - Fortification (spirit addition) - Calculator

someone told me to use this calculator, but I can't figure it out. Any help would be great!

Metalhophead

 

[GilSwillBasementBrews]

Current alcohol is the alcohol your beverage is currently.

Desired alcohol is the abv you are seeking.

Spirit alcohol is the abv of your vodka.

Volume of wine would be your volume of your current beverage.

Volume of spirit. Would be how much of your vodka to add to reach your desired abv