I can’t find button in TinyMCE toolbar for shortcode adding?
Go to menu “Contact Form” > “Settings” > “Form” tab > “Other Settings” section. Option “TinyMCE Support” should be enabled. If this option is enabled, but you doesn’t TinyMCE toolbar button after the page refresh, this is can be related to features of your theme or third-party extentions for TinyMCE editor.
In this case, you can manually add following shordcode into the TinyMCE editor area: [wcp_contactform id="wcpform_1"]. Preferably to add shordcode via TinyMCE “Text” mode and also please clean up form shortcode from extra HTML tags in case if they are present.