Just a disclaimer for those who do not know: Java and Bedrock use different ways to "raise" the shield:
Java: Just hold down the proper mouse button / key.
Bedrock Just hold sneak (which is also fly down), which it then activates after a short pause and until you stop sneaking. (By default on Touch controls it is double-tapping the sneak button to actually toggle sneak.)
With PE 1.10, the shield has finally come to Bedrock as well. But it does not work in PSPE, which knows nothing about this newfound ability of PE...