Yes, finding the exact version of WAS you're running is a dark art.  It's too hidden to bother showing it on the admin pages (sarcasm to IBM intended).
Start  out with:
WRKLNK '/QIBM/ProdData/WebSphere/AppServer/*'
On my 7.4 system I see V85.  Drill into that.
Then you should see what kind(s) you have.  I have Express.  Drill into your kind.
Then select bin.  You will end up with something like:
/QIBM/ProdData/WebSphere/AppServer/V85/Express/bin
Fire up STRQSH
Then modify the following to match your information
/QIBM/ProdData/WebSphere/AppServer/V85/Express/bin/versionInfo
If you get the following message then you <fouled> up when upgrading and ignored prereq's to modify WAS before the upgrade:
/QIBM/ProdData/WebSphere/AppServer/V85/Express/bin/versionInfo: 001-0014 Command /QOpenSys/QIBM/ProdData/JavaVM/jdk626/32bit/bin/
java not found.                                                                                                                  
Well, duh, you're not going to find Java 6 at 7.3 or above.  I did this boneheaded move.
So you're going to have to fix that to use the right java as per
https://www.ibm.com/support/pages/how-fix-websphere-application-server-v85-after-upgrading-ibm-i-v7r3-os
That same link has a back door to find the WAS version:
EDTF '/qibm/proddata/websphere/appserver/v85/Express/properties/version/was.product'
On my system it shows:  <version>8.5.5.8</version>
If you can finally get that versionInfo to work there are flags on the command to show you fix packs and ifixes.  Details at:  
https://www.ibm.com/docs/en/was/9.0.5?topic=tools-versioninfo-command
You'll need to know this for this particular issue!
For more fun:
https://www.ibm.com/support/pages/fix-list-ibm-websphere-application-server-v85
"No man is completely worthless, he can always be used as a bad example."  Sometimes I fit that bill...
Rob Berendt
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