Try this
If the gas oven has weak flames even if it is set to HI, open and close the gas valve 3 to 4 times, remove the
burner cap and burner head, and use a needle to poke the burner hole 5 to 10 times to clean out any debris.
Also check if the gas hose is kinked.
For some built-in products, you will need to push in the knob until flames appear and turn it 90 degrees [9 o'clock position] to set it to HI.
This guide was created for all models, so the images or content may be different from your product.