no, you can't write it yourself...
if they're referring to an agreement, then one should be there somewhere... or at least mentioned as something you need to request be sent to you, signed and returned, before submitting work/ideas...
it's common in the film industry, and i'm not surprised to see the comics biz go the same route... all you need do is call or write that company and request a 'submission agreement' ... then follow their instructions for submitting your work/proposal...
that's how you get it to be 'solicited'...
fyi, that excerpt you quoted above contains this, further down:
"Obtain a copy of the agreement here."
and, below that:
"
View or
download a copy of the Submissions Agreement"
you need to pay better attention to what you're reading...
love and hugs, maia