pip3 install https://github.com/lhelontra/tensorflow-on-arm/releases/download/v2.3.0/tensorflow-2.3.0-cp37-none-linux_armv7l.whl
でOK
ImportError: libopenjp2.so.7: cannot open shared object file: No such file or directory
と言われたので
apt-get install libopenjp2-7-dev
で解決