You can change BIOS password using iDRAC. This depends on "Password Status" BIOS setting and whether iDRAC have all details on BIOS to change settings. Some times iDRAC will not allow to make BIOS settings if the server is not completely booted.  Can you login to iDRAC and traverse to "System Security" section of "Configuration -> BIOS Settings" page to check current setting for Password Status?

• If this attribute set to Unlocked state then you can change BIOS system and setup password from same page using iDRAC. You no need to enter old password for this option
• If it is set to Locked state then you can change only setup password using iDRAC. In this case you can change "Password Status" attribute first then later once applied use iDRAC only to change both system and setup password

You can use PWD_EN jumper setting to disable the password. You can refer below link to identify jumper location and details on resetting password using jumper. If you use NVRAM_CLR option it will reset all BIOS setting to default including passwords. This should not impact your setting on Power Edge RAID controller like H730, H740, H330, HBA330 etc.

https://www.dell.com/support/manuals/en-in/poweredge-r740/per740_ism_pub/system-board-jumpers-and-connectors?guid=guid-7233c18e-b255-4620-be3d-c1a348083558&lang=en-us 

https://www.dell.com/support/manuals/en-in/poweredge-r740/per740_ism_pub/disabling-a-forgotten-password?guid=guid-0cb73b4f-8b9d-4c1c-a251-9e693591bbe0&lang=en-us