You can find the child theme in the WoodMart theme folder, then upload in Appearance > Themes, upload, using the child theme would not influence the site.
If you have any questions please feel free to contact us.
When i download all files from themeforest i don’t have child theme inside. This is the reason i am writing here. This is what i have inside theme folder: https://gyazo.com/149fdbeb451f858ed183a6a4611a8927
I have another question. I have installed plugin for caching, but when i activate css caching the custom css in theme options is not working. Can you say me where is the file of custom css from the theme, so i will exclude it from caching?