If you didn't have any fancy settings configured previously, the best approach is to first disconnect SharePoint from Office Server and connect it back from scratch. So can do the following:
Remove-SPWOPIBinding -All:$true
Reconnect SharePoint to OWA by running the following. Bear in mind, that this assumes your OWA uses HTTP instead of HTTPS:
New-SPWOPIBinding -ServerName <WacServerName> -AllowHTTP
Get-SPWOPIZone
Set-SPWOPIZone -zone "internal-http"
(Get-SPSecurityTokenServiceConfig).AllowOAuthOverHttp
$config = (Get-SPSecurityTokenServiceConfig)
$config.AllowOAuthOverHttp = $true
$config.Update()
More details in Configure Office Online Server for SharePoint Server
Alternatively, you can try the following command:
New-SPWOPIBinding -ServerName "Server.corp.Contoso.com"
This example creates bindings for all the applications and file name
extensions that the WOPI application supports on the current
SharePoint farm where this cmdlet is run.