If this is a Trial edition, then to export you need to

a) convince someone in WRI Sales to get you an Export-enabled license, or

b) check with the university IT office if a regular copy of Mathematica is available through the university.

From Help:

The currently supported export formats:

In[1]:= $ExportFormats

Out[1]= {"3DS", "ACO", "AIFF", "AU", "AVI", "Base64", "Binary", "Bit", "BMP", "Byte", \
"BYU", "BZIP2", "C", "Character16", "Character8", "Complex128", "Complex256", \
"Complex64", "CSV", "DICOM", "DIF", "DIMACS", "DOT", "DXF", "EMF", "EPS", \
"ExpressionML", "FASTA", "FITS", "FLAC", "FLV", "GIF", "Graph6", "Graphlet", \
"GraphML", "GXL", "GZIP", "HarwellBoeing", "HDF", "HDF5", "HTML", \
"Integer128", "Integer16", "Integer24", "Integer32", "Integer64", "Integer8", \
"JPEG", "JPEG2000", "JSON", "JVX", "KML", "LEDA", "List", "LWO", "MAT", \
"MathML", "Maya", "MGF", "MIDI", "MOL", "MOL2", "MTX", "MX", "NASACDF", "NB", \
"NetCDF", "NEXUS", "NOFF", "OBJ", "OFF", "Package", "Pajek", "PBM", "PCX", \
"PDB", "PDF", "PGM", "PICT", "PLY", "PNG", "PNM", "POV", "PPM", "PXR", \
"QuickTime", "RawBitmap", "Real128", "Real32", "Real64", "RIB", "RTF", "SCT", \
"SDF", "SND", "Sparse6", "STL", "String", "SurferGrid", "SVG", "SWF", \
"Table", "TAR", "TerminatedString", "TeX", "Text", "TGA", "TGF", "TIFF", \
"TSV", "UnsignedInteger128", "UnsignedInteger16", "UnsignedInteger24", \
"UnsignedInteger32", "UnsignedInteger64", "UnsignedInteger8", "UUE", \
"VideoFrames", "VRML", "VTK", "WAV", "Wave64", "WDX", "WMF", "X3D", "XBM", \
"XHTML", "XHTMLMathML", "**XLS**", "**XLSX**", "XML", "XYZ", "ZIP", "ZPR"}

But in his attached notebook it says "Export is not available in this version of the Wolfram Language", so probably he is using a trial version.