Can’t update to ios13 needed for Netflix install

Not possible. Netflix requires iOS/iPadOS13 or later.

An iPad Air1, mini2 or mini3 can only be updated to iOS 12.5.

Apple ended major update support for these models of iPad in September 2019. Whilst these models have since continued to receive “point” security updates, they cannot be updated to iPadOS 13 (or any later major versions of iPadOS) as the internal hardware does not meet the minimum technical requirements (RAM and CPU) for newer versions of iOS/iPadOS.

Some App developers have dropped support for iOS versions preceding iOS 13.x for technical reasons (often because APIs or software libraries upon which they rely have been updated in the new version of iPadOS, making their App incompatible with earlier versions). 

Whilst many App titles remain compatible with your iPad, if you want or need to access to Apps requiring the most recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model that supports iPadOS14.

Sorry, I appreciate that this may not be what you were hoping to learn.

I hope this information provides helpful clarity as to your available options - and the limitations of your existing iPad.

You can't any longer.

Sorry.

Your over 7-year old iPad Air model cannot ever upgrade beyond some version of iOS 12, currently at iOS 12.5.

The internal hardware in that iPad is too old, too underpowred and is not capable of running all of the new, advanced and internal hardware resource intense features of iPadOS.

Sorry.

If you need/want an iPad with an up to date iPadOS with access to current, updated apps, then you really need to seriously consider a new iPad model OR a much “newer” , used iPad model capable of running the latest iPadOS versions.

There are plenty of newer, older iPad models that can run the latest, current versions of iPadOS.

Sorry & Best of Luck to You!

I want to download iOS 12.5

What iPad year and model do you own and what iOS is this iPad currently running?

What iPad?

Actually, there is a way IF you own a much newer iOS device, like a newer/new-ish iPhone.

Do you own a newer-ish iPhone?