The standard BIOS Y2K fix implementation for BIOS is to check at power-up or system restart if the stored current century is set to 19 and the real-time clock date field indicates 00 or 01. It is then assumed that the 21st century has begun, and BIOS then re-sets the current century to 20. In addition to that, the runtime BIOS call "get date" adjusts its result fields in the same way, so that operating systems using BIOS time and date functions display a correct date. Modern operating systems access real-time clock and century storage directly, and have to take care of the situation themselves. Finally, the BIOS Setup screen allowing to set time and date must have a four-digit year field.
Extended Y2K support means that BIOS updates the internal century storage not only at boot time, but also when the runtime BIOS call is invoked.
If the BIOS does not begin an automatic century update user interaction is needed. Enter BIOS Setup, and adjust the year from 1900 to 2000. Since the location the century is stored in is never touched by the real-time clock, the change is permanent. The same task can be fulfilled from whatever software allows to adjust system time and date, as long as this software has a four-digit year count.