The Manage-bde.exe command-line tool can be used to replace TPM-only authentication mode with a multifactor authentication mode. For example, if BitLocker is enabled with TPM authentication only and PIN authentication needs to be added, use the following commands from an elevated command prompt, replacing 4-20 digit numeric PIN with the desired numeric PIN:
manage-bde.exe -protectors -delete %systemdrive% -type tpm
manage-bde.exe -protectors -add %systemdrive% -tpmandpin <4-20 digit numeric PIN