The My Dell and Dell Power Manager apps are only compatible with Dell Inspiron, Vostro and XPS laptops, they cannot be installed on your laptop model.
There is no native setting in Windows to limit the upper charge level on a laptop battery, if you do not have that setting in BIOS - Power Management - Battery / Battery Health Manager, then you will be unable to set the upper limit on the battery charge on your laptop model.
Start your laptop, then on the Dell logo screen, repeatedly press F12 or Fn + F12, then on the resulting menu, open Dell Diagnostics and perform the full diagnostics test, what does that indicate for your battery health.