You must run this script within the PlusWord game iframe. You can either do this in devtools by selecting the PlusWord evaluation context or go to https://puzzles-prod.telegraph.co.uk/plusword/.
The script
for(i=0;i<30;i++){
app.vue.data.active.cell=i;
app.handlers.letterEntered({item: {display: app.vue.methods.getPuzzleObject().cellsSolution[i] }}, null);
}
This is an extremely simple script which loops through each cell and enters the correct letter from cellsSolution. By adding a timeout or a function which takes a cell number you can easily adapt this script to choose a solution time or choose a specific cell to 'solve'.