You can make very quick assignments at any point by left-dragging an NmrResidue or NmrAtom from the sidebar onto one or more selected peaks. If you have made a mistake, simply undo it with Ctrl + Z (Cmd + Z on a Mac) or drag a different NmrResidue/Atom onto the peak. If you wish, you can select multiple peaks in multiple spectra and/or displays and drag and drop NmrResidues or NmrAtoms onto them all in one go - just make sure you do the drop on top of one of the peaks.
In some cases you may find that no assignment is made when dragging an NmrResidue onto a selected peak. This may occur when there is an ambiguity about which NmrAtoms in the NmrResidue should be associated with the peak. For example, a Trp residue contains a side-chain NH group (NE1/HE1) as well as the backbone NH group. In this case you need to drag the desired NmrAtoms onto the selected peak rather than the whole NmrResidue.
Note that if you have not selected any peaks, dragging an NmrResidue or NmrAtoms onto your display will place marks at the chemical shifts associated with the NmrResidue or NmrAtoms.
If the assignments for your protein's HSQC are already available, you can quickly add these to a spectrum in Analysis in the folowing way:
Load your HSQC spectrum by dragging it into the drop area. Peak pick the spectrum, e.g. by holding down Shift + Ctrl (Shift + Cmd on a Mac) while left-dragging the mouse over all your peaks.
Load your protein sequence by dropping a FASTA file into your project. Create a new NmrChain by opening up the NmrChains in the sidebar and double-clicking on New NmrChain. Select Clone from Chain and select the Chain that was created when you loaded in your sequence. Now you have a new NmrChain containing your full protein sequence. You can then assign your HSQC directly, by selecting each peak and dragging the correct NmrResidues onto it.