Can anyone help please!

Please can anyone help me! I am not a wordpress expert but I know my way around, my site https://www.salamandar.co.uk/ was built for me, all I have tried to do was install a plugin (https://www.ads-software.com/extend/plugins/si-contact-form/installation/) and my site has totally crashed, it has an error message on the home screen. :(( Please help someone!

Thanks in advance!