That plant is too young to be worried about fertiliser in a soil. A decent compost (and the seed itself) will contain every the plant needs for at LEAST 2 weeks, even up to a month. Just give it plain water. Rain water preferably, but normal tap water will do. If you can leave tap water in an open container overnight to evaporate some of the nasties before you water, even better. Soil is so forgiving, the biggest danger is killing you seedling with kindness.