To lock a layer, follow these steps:

1. Expand the Layers https://cdn.elev.io/file/uploads/Nx6j1ilgYkjKwwUzxKv9Jx2yWyIGUZG4VbEE9W71H30/aZSOeDl3ASq1ED49iBbgy2zh8WS8mGtounuMAdwnkIk/layers-aAU.png tool from the right toolbar.

2. Select the layer you wish to lock and click the Lock button.

https://cdn.elev.io/file/uploads/Nx6j1ilgYkjKwwUzxKv9Jx2yWyIGUZG4VbEE9W71H30/ir1o7ZLRpjXQwOCDdPhKe8qhxMjzQRKxZNJZuQCu48Q/Locking a layer.fw-eak.png