This has been covered before (see similar threads at bottom of current page), but I've never seen a cheap easy way of doing it other than replace the assembly which I think costs $700 and are not stocked anymore (!). Some people say they glue it back down but they don't say what with and whether you glue all over it or just at the edges. Maybe a hot air gun could be used to soften it to help it back. Some styles of airbags have the complete front cover hinged so it lifts up when deployed whilst others simply rip and burst from their containers, so you'd really want to know exactly what is what.
I do know that you don't turn the ignition on if the airbag is removed as this sets a fault which can only be erased by a Tech1 tool.
Sorry I cannot be of more help.
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