Here’s a video that shows the disassembly of a MSI GL62M laptop that may help.
At 6:40 minutes into the video the fans and heat sink can be seen being removed from the GPU and CPU. The CPU and GPU are visible at 7:09 minutes. Just disassemble enough so that the fans and heatsink can be safely removed etc
Here’s the ifixit How to Apply Thermal Paste guide. Even though it shows it being done on a different make and model laptop, the procedure for refreshing the thermal paste is the same. Here’s another link that may also help.
Note: it is always prudent to remove or disconnect the battery as soon as it is accessible so as to minimize any possible electrical problems before doing anything else when working inside a laptop. Even though the laptop is off, there is always power available at certain points on the motherboard when the battery is connected. The Power On/Off button is not a power isolating button. It merely signals the BIOS as to the user’s intentions. Think of the laptop as being in an extremely low power state rather than being completely off and disconnected from the power when turned off.
The battery can be seen being removed at 3;30 minutes into the video. Reconnect the battery as late as possible when closing the laptop for the last time after completing the task.
Wearing a wrist strap connected to earth also helps to prevent ESD damage to any sensitive components that you may accidentally contact during the procedure.
Mechanical damage i.e. slipping when using tools and physically damaging components, is another problem - be careful with tools and be gentle. If you run into any problems - stop and think about it before proceeding - rather than getting frustrated and possibly causing damage.
Hopefully this is of some help.