I did that a few times early-on (now I prefer transferring to PayPal). If I remember correctly, I would receive an email from ibotta with a redemption code. I would then add the funds to my amazon account by choosing "redeem gift card" in my account.
You should get an email from Ibotta with your amazon e gift card #, you can click on the link that will take you to your amazon account /adds it automatically or you can copy and past the e gift card # they provide in the email and then paste it into your amazon account (amazon.com acct-my account-manage gift card balance-redeem a gift card)
Go into your amazon account and click on gift cards then you will have an option to add a gift card to your account and it will be stored there until you want to use it. Or when purchasing something you can enter it while checking out.
If you have a Prime account, you can “load a gift card” to your saved account. Click on the icon “gift cards” and from there the “load a gift card.” Input the number code. If you don’t have Prime, you can simply input the number when you checkout.
You can load it to stack up or put the code in under payments when you check out. Go to Account, gift card balance to redeem and it will show you how much you have when you got them and what you've spent them on.