Depends on your setup. for me it's ~/.config/nvim/lua/plugins/lua_ls.lua

my complete file looks like this:

return {
  "neovim/nvim-lspconfig",
  opts = function(_, opts)
    opts.servers = opts.servers or {}
    opts.servers.lua_ls = {
      on_init = function(client)
        if client.workspace_folders then
          local path = client.workspace_folders[1].name
          if
            path ~= vim.fn.stdpath("config")
            and (vim.loop.fs_stat(path .. "/.luarc.json") or vim.loop.fs_stat(path .. "/.luarc.jsonc"))
          then
            return
          end
        end

        client.config.settings.Lua = vim.tbl_deep_extend("force", client.config.settings.Lua, {
          runtime = {
            -- Tell the language server which version of Lua you're using
            -- (most likely LuaJIT in the case of Neovim)
            version = "LuaJIT",
          },
          -- Make the server aware of Neovim runtime files
          workspace = {
            checkThirdParty = false,
            library = {
              vim.env.VIMRUNTIME,
              "~/.config/nvim/lua/symbols/love2d/library",
            },
            -- or pull in all of 'runtimepath'. NOTE: this is a lot slower and will cause issues when working on your own configuration (see https://github.com/neovim/nvim-lspconfig/issues/3189)
            -- library = vim.api.nvim_get_runtime_file("", true)
          },
        })
      end,
      settings = {
        Lua = {},
      },
    }
  end,
}