ok, tested and works!!!!
go to tools-> configure external tools-> add
title: usb hid bootloader (moved entry point + $800)
program filename:C:\Users\user\AppData\Local\Arduino15\packages\stm32duino\tools\win\hid-flash.exe
parameters: $ProjPath()$NameOnly($ProjFile()).bin com1
check "scan output for fpc messages"
and in project->project options->compiling and linking->
check the "pass option to linker -k delimiter is space"
add this text: "-Ttext=0x08000800"
now, set jumper boot1 to 1 in the bluepill board. connect to computer using usb cable and you can flash it. after that, unplug the usb cable, set boot1 jumper to 0.
thats all
caution! bootloader set microcontroller hardware to do the job. this settings are not undoed and can affect your program behavior. verify it