is an expression that is constructed with the 格助詞（かくじょし） (case marking particle) で, and the potential form of the い-Adjective いい
, よければ. The literal meaning of ‘if with (A) is good/fine’, or ‘if by (A) is good/fine’ is quite similar to the standard translation, which is ‘if (A) is ok’.
will always follow nouns or noun-phrases.
If yakiniku is fine, there is a good yakiniku place near my house, so do you want to go there?
If used ones are fine, we have many good options.
is a phrase that is often used in relation to oneself, in order to politely offer some sort of help, advice, or service.
If you don't mind, I can help you. (If I am a suitable option, I can help you)
If you don't mind, I can take a picture for you.
is being used in its standard meaning of ‘with’ or ‘by’, でよければ
implies that the speaker is enquiring whether the quality/ability of (A) is good enough to achieve some specific result.