Here is the Dell Bios recovery options/procedures. If you are lucky one of them will apply to your system. If not the other option, sadly, is motherboard replacement. https://www.dell.com/support/article/us/en/19/sln300716/bios-recovery-options-on-a-dell-pc-or-tablet?lang=en Also here is the Dell policy on a BIOS corruption. https://www.dell.com/community/Product-and-Support-Issues/Dell-Policy-BIOS-breaks-motherboard-CMOS/m-p/5741766#M3962

they does't work .. 

motherboard replacemente for an bios update failure ?!?!?!

oh my god !!!

Sadly, that is the only recourse if there is no BIOS recovery for your specific model.  Its been this way for years on Dell's and only lately that they offer BIOS recovery on some models.  This is the same on some other brands, not just a Dell only issue.

For this reason I (and most of the other techs on here) only recommend a BIOS update if its absolutely the last option.  

Yup, BIOS updates are incredibly risky with Dell products. 

I wish they would at least indicate some sort of warning on the driver download page or in the driver description. Most people have trust that Dell wouldn't release an update that can break their system...but are met with a slap in the face and buyers remorse after bricking their expensive paper weight.