First Release

Download AIDA64 from the Play Store, go to the CPU section and find the ‘Instruction Set’ field.

It will list either one of those three:

64-bit ARMv8-A
64-bit ARMv8-A (32-bit Mode) which is ARMv7-A.
32-bit ARMv7-A (legacy)
Examples:

64-bit ARMv8-A:

64-bit ARMv8-A running in legacy 32-bit mode:

32-bit ARMv7-A mode (legacy):