Unable to update Find My iPhone on my iPad 2

I have an iPad 2 with capacity 12.8 GB and 5.5 GB available. An update is available for Find iPhone to version 4.0 but I am unable to install that update. I have IOS operating system 9.3.5. it's time I try to update I am presented with unable to download app find my iPhone could not be installed at this time I choose we try and get the same response each time. I have tried changing Wi-Fi networks to my guest Network and my Android hotspot. I've turned off find my iPhone and turned it back on I have restarted the iPad multiple times and make sure it is charged to 100% what solution might I be missing?

BTW I know that this is a very old device however I also know that the battery seems to last forever I have not charged it for over 7 months and when I opened it and turned it on to check for updates it was at 68%, in contrast to my iPad pro which does not even hold a battery charge for 4 days turned off or a full day if turned on. I often take an older device with me camping for my grandson to use to watch movies very frustrating that I can't update this app.

[Re-Titled by Moderator]