The function cdsbootstrap uses matlab's very common Name/Value pair syntax. Read the first few lines here:
Specify optional comma-separated pairs of Name,Value arguments. Name
is the argument name and Value is the corresponding value. Name must
appear inside single quotes (' '). You can specify several name and
value pair arguments in any order as Name1,Value1,...,NameN,ValueN.
So if you wanted ALL default values, you would use the call:
[ProbData,HazData] = cdsbootstrap(ZeroData,MarketData,Settle);
If you wanted to change one of these possiblities you would simply include the name and value, all names omitted are set to defaults. Based on your value of 0.25 I'm going to assume you are trying to set the RecoveryRate since 0.25 is close to the default.
[ProbData,HazData] = cdsbootstrap(ZeroData,MarketData,Settle,'RecoveryRate',0.25);
Ref:
http://www.mathworks.com/help/fininst/cdsbootstrap.html