For Itl Models - Lenovo IdeaPad 3 Series Hardware Maintenance Manual

Figure 22. Disconnect the battery pack cable
Step 2. Loosen four screws and then remove the heat sink.
Figure 23. Loosen four screws and remove the heat sink
Screw specifications
M x L
Go to https://support.lenovo.com/partslookup
replacement part:
Heat sink

For ITL models

Make sure the following FRUs (or CRUs) have been removed.
44
IdeaPad 3/IdeaPad 3i/IdeaPad Slim 3/IdeaPad Slim 3i series Hardware Maintenance Manual
Number of screws
4
to look up the Lenovo part numbers of the following