This will never be possible.
Your iPad model cannot upgrade/update beyond any version of iOS 12, currently at iOS 12.5.1
The 2013 iPad Air 1, iPad Mini 2 and 2014 iPad Mini 3 cannot upgrade beyond any version of iOS 12.
These iPad models have overall internal hardware that is too old, too underpowered and incapable of running all of the new, advanced and internal hardware resource intensive features of iPadOS.
These iPad models will be 7 snd -years old, this year, in 2021.
Sorry.
It's 2021, now.
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 purchase of a new iPad model OR a much, MUCH “newer” and less expensive, used iPad models, from better known, trusted sources, like other Apple product/device retailers/resellers, locally or online, 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!