I updated the software of my ipad to be ios 8.4.1 but I wanted to return it to ios 8.4 how can I do it?

Today I updated my software to ios 8.4.1 but I need to return it to ios 8.4 I have an I pad mini the storage capacity is 16G the problem is that I need to download app but it couldnt be downloaded because the ios has to be 8.4 so I need to unupdate my software and I needed to know how can I do that and can you help me or not?

Please answer me as soon as possible if you can answer today or even right now please do that