So, the app offers us the most obvious first method:
Loot diamonds from fish. You can bait them, collect coins from them periodically and finally sell them at an increased value. However, this option has an obvious disadvantage - time-consuming. Actually, therefore I offer you the next way. (p.s. this way you can add not only the cherished coins, but also increase the level, if you need it for some reason)

Find our game in the steam library, right-click -> properties

Go to “installed files” -> Browse. The folder with the game will open. Look for a txt file called “save” in the folder, its size is a little less than 3kb.

Click. A notepad will open, look for the line “_gold” in it. (For convenience, you can search using CTRL+F). The number after it indicates the number of diamonds. We write as many as we want. (p.s. to increase the level we do the same thing, but we’re looking for exp, not gold)

We MUST save changes to the file.Then you can launch the game.

Congratulations! Now you don't have to choose between a kitty and a dog anymore - you can buy them all!!! (๑˃ᴗ˂)ﻭ