I keep watching youtube videos of cute slow lorises kept as pet. When they enjoy on being tickeled and raise their arms, it is so good to watch. I am planning to adopt a slow loris as pet. I want some advice as to how to properly take care of a pet slow loris?
Unfortunately, there is no way to properly keep a slow loris as a pet.
This is for several reasons: as nocturnal animals with huge eyes, the bright lights of human houses cause them pain. As animals frequently on the move, being trapped in a tiny cage is unhealthy. Even the tickling behavior you mention is not so cute--a slow loris raises its arms when it is terrified and trying to defend itself. Additionally, while you don't state your location, it's unlikely they are legal to keep where you live as many countries do not allow keeping endangered species as pets.
Here are some resources as to the reality of owning a pet slow loris.
The Internation Animal Rescue Organization has good information about the dangers of owning one:
Slow lorises have a venomous bite that is harmful to humans. Usually their teeth are clipped but if their teeth are still intact they mix venom secreted from a gland inside their upper arm with saliva to deliver a venomous bite. This can cause anaphylactic shock and even death in humans.
National Geographic has resources on the cruelty involved in purchasing one:
Before [the animals are] sold, most undergo a painful process to remove their sharp teeth—and circumstances don’t improve from there. In a 2016 study, researchers from Oxford Brookes University examined a hundred online videos of pet lorises and concluded that all the animals were distressed, sick, or exposed to unnatural conditions.
While slow lorises are adorable animals, and I understand why you'd be interested in one based on the videos online, it's important to understand that these videos actually show acts of animal neglect and that the slow loris does not make a good pet. I recommend doing research on other species instead--there are plenty of wonderful mammals that do well in captivity, and whose purchase doesn't contribute to the problems involved in the slow loris trade.