Can you add your board reference and more details about your issue.
Add an external pull-down resistor.
Thank u for reply.which Pin i put resistor boot pin or PB14
Pulldown resistor won't help, bootloader holds PB14 (and PA6) hard high, see AN2606, footnote to the table for given model.
There's no workaround - if you can't avoid boot mode, you have to design your system with this problem in mind.