how to set text button agree in license dialog

help me!
how to set text button I Agree in license dialog

standard:

Page License LicenseShow
Function LicenseShow
    GetDlgItem $R0 $HWNDPARENT 1
    SendMessage $R0 ${WM_SETTEXT} 0 "STR:My Text"
FunctionEnd 

MUI:

!define MUI_PAGE_CUSTOMFUNCTION_SHOW LicenseShow
!insertmacro MUI_PAGE_LICENSE "license.rtf"
Function LicenseShow
    GetDlgItem $R0 $HWNDPARENT 1
    SendMessage $R0 ${WM_SETTEXT} 0 "STR:My Text"
FunctionEnd