This is on the underside of the head, and I used double sided tape to hold it in position (see photos). Obviously a cleaner more permanent repair could be made, but Ive left it like this so the chin guns can be changed if required.
They are all a push fit, so not hard to reassemble. The item "STAR WARS ESB VINTAGE AT-AT VEHICLE UNBOXED WORKING" is in sale since Monday, July 1, 2019. This item is in the category "Toys & Games\Action Figures\TV, Movies & Video Games". The seller is "janeway63" and is located in East Boldon, Tyne & Wear. This item can be shipped to United Kingdom, Antigua and barbuda, Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Australia, United States, Canada, Japan, New Zealand, China, Israel, Hong Kong, Norway, Indonesia, Malaysia, Mexico, Singapore, South Korea, Switzerland, Taiwan, Thailand, Bangladesh, Belize, Bermuda, Bolivia, Barbados, Brunei darussalam, Cayman islands, Dominica, Egypt, Guernsey, Gibraltar, Guadeloupe, Grenada, French guiana, Iceland, Jersey, Jordan, Cambodia, Saint kitts and nevis, Saint lucia, Liechtenstein, Sri lanka, Macao, Monaco, Maldives, Montserrat, Martinique, Nicaragua, Oman, Pakistan, Paraguay, Reunion, Turks and caicos islands, Aruba, Saudi arabia, South africa, United arab emirates, Ukraine, Chile.